Robert T. Novotnak

High-performance nonlinear feedback control of a permanent magnet stepper motor

The permanent magnet stepper motor is considered for use in high-performance positioning systems. A model-based control law is developed using the exact linearization methodology and implemented on an industrial setup. The practical issues of speed estimation and voltage saturation are considered and resolved through the use of a nonlinear observer and field-weakening, respectively. The results of the implementation of the control algorithm for an industry-specified point-to-point move of a linear positioning table are presented and discussed. >

High-performance induction motor control via input-output linearization

We have shown that a current-command input-output linearization controller can achieve high-performance motion control, that is, the precise tracking of a fast point-to-point position reference. Specifically, this controller was shown to provide the means of decoupling the speed and flux dynamics in an induction motor. This decoupling of speed and flux was exploited to simultaneously track the position/speed reference and an optimal flux reference. This flux reference was used to obtain the optimal (max/min) motor torque at any given speed without violating voltage and current limits. Experimental results were presented to demonstrate the effectiveness of this scheme.<<ETX>>

A systematic approach to selecting flux references for torque maximization in induction motors

This paper addresses the problem of optimal selection of the flux reference in induction machines. The results are based on a standard differential equation model of the induction machine and give the value of the flux reference which maximizes the torque at constant speed subject to voltage and current limits. Both the motor and generator modes are considered. The formulas are useful for the real-time programming of digital controllers designed to achieve maximum performance of AC drives at high speeds. Experimental results are given to validate the analysis and demonstrate the usefulness of the optimal flux reference in high-performance servo applications.

Nonlinear speed observer for high-performance induction motor control

In this paper, we consider the problem of estimating the angular velocity of an induction motor using encoder measurements. Two methods are compared. In the first method, the speed is found by calculating the backward difference of the position measurement and low-pass filtering the result. In the second method, the velocity is estimated using a nonlinear observer constructed using the known dynamic model of the induction motor. The performance of the two methods is evaluated in the context of their use for velocity feedback in a high-performance field-oriented control law. Experimental results demonstrate that the speed observer leads to a smoother operation of the motor in closed-loop. With the estimator based on differentiation, either the delay imposed by the low-pass filter is too large to maintain high bandwidth feedback, or the fluctuations in the estimated speed are so large that much more energy ends up being dissipated to achieve the same control task. >

Nonlinear speed observer for the PM stepper motor

A nonlinear observer for the permanent magnet (PM) stepper motor is considered. Specifically, the method of A.J. Krener and W. Respondek (1985) is used to construct a nontrivial full-order speed observer that has linear error dynamics. The procedure is validated by experimental results. Reduced-order observers are constructed by inspection. >

High performance motion control of an induction motor with magnetic saturation

This work generalizes the authors work on high-performance control of induction motors to machines that exhibit significant magnetic saturation. The controller design is based on the standard d-q model of the induction motor which has been modified to account for the saturation of the iron in the main (magnetic) path of the machine. An input-output linearization controller is used to provide independent (decoupled) control of the speed and flux. With this controller, the flux reference becomes an extra degree of freedom for the designer to help achieve performance objectives. Taking into account saturation, the flux reference is chosen to achieve the optimal torque at any given speed. Experimental results are given to demonstrate the input-output controllers effectiveness in providing the tracking of a given position and speed trajectory while simultaneously tracking the optimal flux reference.

High performance nonlinear feedback control of a permanent magnet stepper motor

How modern theories of nonlinear control can be applied to problems of current industrial interest is illustrated. The tracking of trajectories that pushed the system to the limits of performance is considered. As the experimental results show, very good tracking performance was obtained. The results, having been obtained with an experimental setup that is only slightly modified from an existing motion control product, bear direct relevance to current industrial practice.<<ETX>>

Comments on "Passivity-based control of saturated induction motors"

The authors comment on the paper by L.U. Gokdere et al. (see ibid., vol. 48, p.870-2, 2001). A review of the experimental evidence shows that passivity-based control of saturated induction motors does not provide superior performance over input-ouput linearization. Higher tracking errors can be observed and traced to the open-loop nature of the flux controller. In contrast, input-output linearization controllers achieve close tracking of flux, speed, and position references for the most demanding trajectories.

Comments on "A passivity-based method for induction motor control" [with reply]

In the paper by L.U. Gokdere and M.A. Simaan (see ibid., vol. 44, p.688-95, 1997), a comparison is made between a passivity based controller and an input-output linearization controller. We point out that this comparison is not valid as the same trajectory was not used for both controllers. The original authors reply to this comment pointing out that there is experimental evidence demonstrating the benefits of the passivity-based controller developed for induction motors. These include closer tracking of the same mechanical trajectory, and less sensitivity to magnetic saturation, when compared with the input-output linearization controller.